Search Results

You are looking at 91 - 100 of 1,093 items for :

  • Refine by Access: All x
Clear All
Free access

Julián Miralles, Raquel Valdes, Juan J. Martínez-Sánchez, and Sebastián Bañón

registered data of substrate temperature with two temperature probes (Termistor 107; Campbell Scientific, Ltd.) per treatment and volume water content (θ) with five EC-5 soil moisture sensors (Decagon Devices, Ltd., Pullman, WA) per treatment. The EC-5 probes

Full access

Jeffery C. Kallestad, Theodore W. Sammis, John G. Mexal, and John White

Optimal pecan (Carya illinoiensis) production in the southwestern United States requires 1.9 to 2.5 m of irrigation per year depending on soil type. For many growers, scheduling flood irrigation is an inexact science. However, with more growers using computers in their businesses, and with soil moisture sensors and computerized data-collection devices becoming more inexpensive and accessible, there is potential to improve irrigation and water use efficiencies. In this project two low-cost soil monitoring instruments were introduced to a group of pecan producers. They were also given instruction on the use of Internet-based irrigation scheduling resources, and assistance in utilizing all of these tools to improve their irrigation scheduling and possibly yield. The objectives were to determine whether the technology would be adopted by the growers and to assess the performance of the sensors at the end of the season. Three out of the five growers in the project indicated they used either the granular matrix (GM) sensors or tensiometer to schedule irrigations, but compared to the climate-based irrigation scheduling model, all growers tended to irrigate later than the model's recommendation. Graphical analysis of time-series soil moisture content measured with the GM sensors showed a decrease in the rate of soil moisture extraction coincident with the model's recommended irrigation dates. These inflection points indicated the depletion of readily available soil moisture in the root zone. The findings support the accuracy of the climate-based model, and suggest that the model may be used to calibrate the sensors. Four of the five growers expressed interest in continued use of the tensiometer, but only one expressed a desire to use the GM sensor in the future. None of the participants expressed interest in using the climate-based irrigation scheduling model.

Full access

B.L. Upchurch, D.M. Glenn, G. Vass, and W.A. Anger

A unique sensing system is described using an ultrasonic transducer for measuring tree trunk diameters in the orchard. Trunk diameters were calculated from the time it took sound waves to travel from the transducer to the trunk and back to the sensor. The device was calibrated with objects ranging in diameter from 1.6 (0.63 inch) to 19.0 cm (7.5 inches). The distance between the transducer and object was reduced as the diameter increased and was highly correlated (P = 0.99) with actual diameter. The ultrasonic tree diameter sensor exhibited a mean error of 0.04 cm.

Free access

Nicholas J. Flax, Christopher J. Currey, Alexander G. Litvin, James A. Schrader, David Grewell, and William R. Graves

× hortorum L.H. Bailey ‘Pinto Premium Deep Red’) in a soil moisture sensor–controlled irrigation system were polylactic acid (PLA; commercial bioplastic), lignin powder, soy polymer with adipic anhydride (SP.A), BioRes (BR; a refined coproduct of corn

Free access

Mark V. Yelanich, James E. Faust, Royal D. Heins, and John A Biernbaum

The measurement of evaporation and transpiration from container-grown crops is labor intensive and expensive if measurements are made by periodic weighing of the plants with electronic scales. Thin-beam load cells (LCL-816G, Omega Engineering) measured with a datalogger provides a method of making continuous mass measurements over time. Four load cells were tested to determine the feasibility for use in greenhouse studies. The sensors were calibrated to an electronic scale at a range of air temperatures. The electrical signal (μV) was a linear function of mass from 0 to 816 g. The change in mass per change in electrical signal (i.e. the slope) was the same for all four load cells (1.26 g ·μV-1), however the absolute electrical signal (the intercept) was unique for each sensor (-246 to + 101 g). The effect of temperature on sensor output was unique for each sensor in terms of both the magnitude and direction of change. A two-point calibration of mass performed at a range of temperatures is required to properly use thin-beam load cells to continuously measure evapotranspiration of container-grown crops.

Free access

Susan L. Steinberg, Gerard J. Kluitenberg, and Soheni Tanzeema

Little attention has been paid to how the presence of roots influences water content measurements obtained with water content sensors. This issue is especially important if sensors are deployed in densely rooted soil or growth media. This work addresses the impact of roots on water content measurements obtained with dual-probe heat-pulse (DPHP) sensors. In the DPHP method, the maximum temperature rise in response to heating (Tmax) is used to calculate volumetric heat capacity, which in turn is used to calculate volumetric water content. The accuracy of DPHP sensors was evaluated in unrooted and rooted 0.25–1 mm baked ceramic aggregate. For both restricted and unrestricted volumes of aggregate the presence of roots caused DPHP sensors to consistently overestimate water content by 0.05–0.09 cm3·cm-3. Measured values of Tmax were lower in the presence of roots, which resulted in overestimation of volumetric heat capacity that was attributed to the high specific heat of water contained in roots in addition to that contained within the aggregate. Differences in water content and aggregate heating between unrooted and rooted aggregate equilibrated to the same matric potential were less distinct in unrestricted volumes, where the decrease in bulk density has the offsetting effect of lowering the heat capacity. Error in water content caused by the presence of roots and changes in bulk density was estimated by developing a theoretical mixing model for volumetric heat capacity that accounted for the heat capacity of all constituents, including aggregate, water, root water, and root tissue. Predicted errors in volumetric water content due to changes in bulk density or changes in heat capacity due to roots agreed well with direct measurement.

Full access

Sueyde Fernandes de Oliveira Braghin, Simone C. Mello, Jéssika Angelotti-Mendonça, Keigo Minami, and Yuncong C. Li

greenhouse was controlled by an environmental control system with sensors connected to a datalogger (Campbell CR10), which recorded mean, maximum, and minimum temperatures of 22.9, 32.3, and 18.6 °C, respectively, and 70.7% of mean relative humidity and 10

Open access

Tamara Wynne and Dale Devitt

assessed by using sap flow sensors ( Litvak et al., 2012 ; Pataki et al., 2011 ; Peters et al., 2010 ) in conjunction with assessments of environmental demand but typically not with a tight water balance that accounts for irrigation, evaporation, and

Open access

Qiang Liu, Youping Sun, James Altland, and Genhua Niu

, day and night temperature was 25.0 ± 4.2 °C (mean ± sd ) and 17.2 ± 4.2 °C, respectively. Photosynthetic photon flux was measured with a quantum sensor (Apogee Instruments, Logan, UT). Daily light integral inside the greenhouse was 9.5 ± 4.2 mol·m −2

Free access

David A. Grantz and Larry E. Williams

Leaf area development and canopy structure are important characteristics affecting yield and fruit quality of grapevines. Trellising systems and wide row spacing are common viticultural practices that violate key assumptions of currently available indirect methods of leaf area determination. We have developed a protocol for using a commercially available instrument to determine leaf area index (LAI) indirectly in a trellised vineyard. From knowledge of plant spacing, leaf area per vine can be calculated as required. A derived calibration equation resulted in a near 1:1 relationship (y = 0.00 + 1.00 X; r2 = 0.998) between actual and indirectly determined LAI over a range of LAI induced by irrigation treatments. The protocol involved covering 75% of the sensor with a manufacturer-supplied field of view delimiter and masking data from the outer three (of five) concentric radiation sensors. The protocol could form the basis for a general measurement technique, but may require local calibration.